The fast part brings me to my next point - while we can get away with running massive frameworks that take several seconds to render, trying to pull this off is a death knell for your web app (especially if its not an AJAX call). In my experience anything longer than five seconds is a deal-breaker. Worse, loading an entire javascript framework like jQuery or MooTools is probably not a wise choice - they're heavy frameworks and are expensive to process on limited-speed devices.
So I guess my question is: what would you consider to be the best framework for development in this situation? A few people have told me that we just shouldn't use a framework, period, but I find that over the top - is it time for a super lightweight PHP framework specifically geared for mobile web app design?
Thoughts?